PURPOSE: To evaluate the accuracy of preoperative computed tomography (CT) in predicting the location and type of ductal involvement and malignant transformation in intraductal papillary mucinous (IPM) pancreatic tumors and to determine the predictive factors for malignancy at CT. MATERIALS AND METHODS: The helical CT scans obtained in 36 operated on patients with a diagnosis of IPM pancreatic tumor were retrospectively assessed. CT-histopathologic correlation was then performed. RESULTS: The final diagnoses of IPM tumor were combined type (n = 26) and branch duct type (n = 10) lesions. Histologic analysis revealed adenocarcinoma (n = 9), hyperplasia (n = 8), low-grade dysplasia (n = 12), and high-grade dysplasia (n = 7). The lesions were located mainly in the head or uncinate process (n = 20) or were diffuse or multifocal (n = 12). In 12 patients (13 cases), CT-histopathologic correlation was poor, including that in the evaluation of ductal involvement (n = 7), evaluation of lesion location (n = 2), and diagnosis of malignant transformation (n = 4). The most specific predictive signs of malignancy were presence of diabetes and, at CT, a solid mass, main pancreatic duct dilatation greater than 10 mm, diffuse or multifocal involvement, and attenuating or calcified intraluminal content. CONCLUSION: The main causes of poor CT-histopathologic correlation were related to evaluation of main pancreatic duct involvement and diagnosis of malignant transformation. The association between diabetes and specific CT criteria was highly suggestive of malignancy.